SalesTaxCalculator: updated gitignore with jetbrains ide project folder.
SalesTaxCalculator: Product object
SalesTaxCalculator: Abstract sales tax class to calculate sales tax and define interface for sales tax types.
SalesTaxCalculator: basic sales tax includes rate and exempt items.
SalesTaxCalculator: import duty sales tax, includes rate and exempt items
SalesTaxCalculator: tax policy object manages a collection of taxes and can calculate tax on an item.
SalesTaxCalculator: order object manages items, sums total taxes and sums items and taxes to determine total.
SalesTaxCalculator: receipt object presents the order data.
SalesTaxCalculator: the sales_tax_calculator launches examples of the application.